1. Field of the Invention
The present invention relates to a digital demodulating apparatus, a digital receiver, a controlling method of the apparatus, a computer program product, and a recording medium recording thereon the product.
2. Description of the Related Art
In a digital demodulating apparatus including components such as a tuner and demodulator by which a tuning process and a demodulating process are carried out on a received signal, there are cases where the magnitude of a current supplied to a circuit component constituting the tuner or the like is changed.
Japanese Unexamined Patent Publication No. 2001-526485 relates to a receiver which measures a non-linear component in an output signal of a demodulator and controls a bias current of each amplifier stage based on the measurement result. According to this document, the power consumption of the entire receiver is made preferable by controlling a bias current to each circuit element in accordance with the magnitude of a non-linear component in an output signal from the demodulator.
When a supply current to a circuit component is changed, the gain of the circuit component may also be changed. When the gain of the circuit component is reduced, the signal intensity may not be sufficient to perform a demodulating process. On the other hand, when the gain of the circuit component is increased, the demodulating process may not be successfully conducted on account of signal distortion.
The above-described document recites an AGC (Automatic Gain Control) circuit for the purpose of keeping the intensity of a signal supplied to the demodulator to be a predetermined level. The AGC circuit measures the intensity of an output signal from the tuner or the demodulator. When the intensity of the output signal deviates from a predetermined level, the AGC circuit changes the gain of an amplifier or attenuator of the tuner or the like in such a way as to return the signal intensity to the predetermined level. However, since it takes some time to return the signal intensity to the original level by the AGC circuit, the demodulating process may become unachievable during that time.